Pump

ABSTRACT

A SWASH PLATE PUMP HAVING MEANS TO BOOST LIQUID INTO THE LOW PRESSURE PORT OF THE PUMP WHICH COMPRISES, A GROOVE IN THE INTERIOR OF THE PUMP CASING ADJACENT TO THE VALVE AND FACING TOWARDS A SURFACE OF THE ROTARY CYLINDER BLOCK, A CONNECTION ETWEEN THE PUMP INLET PORT AND THE GROOVE AND MEANS TO FEED LIQUID INTO THE CASING TO ENTER THE SAID GROOVE. THE MOTION OF THE CYLINDER BLOCK OVER THE SAID GROOVE IS ARRANGED TO URGE THE LIQUID INTO THE INLET PORT BY VIRTURE OF THE VISCOUS DRAG EXPERTED BY THE CYLINDER BLOCK ON THE LIQUID IN THE GROOVE.

June 13, 1972 D p MCLEOD 3,669,568

PUMP

Filed May 1. 1970 5 Sheets-3heet 1 INVENTOR fio/wu 0 z /armew/z/ By Me 1:00

(7 XU ORW June 13, 1972 o. P. MCLEOD 3,669,568

PUMP

Filed May 1, 1970 5 Sheets-Sheet 2 ik/a7, r JW ATTORNEYS June 13, 1972 D. P. MCLEOD 3,669,568

Filed May 1, 1970 INVENTOR flat Am Parr esowficflv;

ATTORNEYS United States Patent US. Cl. 417-203 7 Claims ABSTRACT OF THE DISCLOSURE A swash plate pump having means to boost liquid into the low pressure port of the pump which comprises, a groove in the interior of the pump casing adjacent to the valve and facing towards a surface of the rotary cylinder block, a connection between the pump inlet port and the groove and means to feed liquid into the casing to enter the said groove. The motion of the cylinder block over the said groove is arranged to urge the liquid into the inlet port by virtue of the viscous drag exerted by the cylinder block on the liquid in the groove.

This invention relates to a pum comprising a rotary cylinder block having cylinders therein either parallel to or slightly inclined to the rotation axis, a cam device, pistons in the cylinders co-operating with the cam device whereby the pistons will reciprocate during cylinder block rotation, valve means co-operating with the block to connect the cylinders during block rotation alternately to a fixed high pressure port and to a fixed low pressure port in the valve means, and a casing at least partially enclos ing the valve means and the cylinder block.

A pump as set out above has the disadvantage at high pump delivery rates and low liquid inlet pressures that the liquid cannot enter the cylinders sufficiently quickly to fill them resulting in cavitation in the cylinders and in the passages carrying liquid to the inlet. It is well known that cavitation can cause damage to a pump and of course it also considerably reduces the operating efliciency. The present invention sets out to provide a simple means to boost inlet liquid pressure into the pump set out above to help to reduce or to prevent cavitation.

In accordance with the present invention a pump comprises a rotary cylinder block having cylinders either parallel to or slightly inclined to the rotation axis, a cam device, pistons in the cylinders co-operating with the cam device whereby the pistons will reciprocate during cylinder block rotation, valve means co-operating with the block to connect the cylinders during cylinder block rotation alternately to a fixed high pressure port and to a fixed low pressure port in the valve means, a casing at least partially enclosing the valve means and cylinder block, a groove in said casing adjacent to the valve means facing towards one surface of the cylinder block, a connection between the said low pressure port and the said groove, and means adapted to feed liquid into the casing whereby liquid may enter the said groove, the arrangement being such that liquid between the said surface of the block and the groove is moved over the said groove by rotation of the cylinder block to increase liquid pressure within the said groove whereby to urge liquid into the said low pressure port.

The means to feed liquid into the casing may comprise centrifugal pumping means formed on the said cylinder block.

The groove may surround the valve means and include a terminal wall adapted to direct liquid. from the groove into the low pressure port.

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The surface of the block rotating over the groove may include vanes and/or indentations which rotate in closely spaced relation with the surface of the said groove.

DESCRIPTION OF THE DRAWINGS One embodiment of the invention for use as a pump will now be particularly described with reference to the accompanying drawings, in which FIG. 1 is a cross-section through the pump,

FIG. 2 is a composite elevation and cross-section showing in part an elevation of the pump and the part sections of the lines lI-A, ll-B and lI-C of FIG. 1,

FIG. 3 is an elevation of the end surface of the cylinder block containing the cylinder ports,

FIG. 4 is an elevation of the structural member showing in particular the flat valve surface, and

FIG. 5 is a developed cross-section taken on the circular line V-V in FIG. 4.

In the drawings the structural member of the pump is an aluminium casting and it comprises three integrally formed parts indicated as the valve 1, the casing 2 and the servo cylinder 3. The valve 1 has a flat valve surface 4 which contains a high pressure delivery port 5 of conventional kidney shape connected to a delivery passage 6 which terminates as a screw-threaded connection (not shown) on the outside of the valve 1. A plurality of mounting lugs 8 are provided around the periphery of the valve 1 for securing the pump in its operative position, the pump being correctly located by a cylindrical boss 9 adapted to fit in a corresponding hole on a driving motor or engine. The hollow casing 2 is closed at the end remote from the valve 1 by means of a cover 11 of pressed sheet metal secured in a large circular recess 12 by means of a circlip 13. A rubber seal 14 ensures a liquid tight connection between the casing 2 and the cover 11.

In the casing 2 a cylinder block 15 of cast iron is arranged for rotation about the axis A-A. The cylinder block 15 includes a fiat surface 16 bearing against the valve surface 4. Within the block there are five regularly spaced cylinders 17 all of whose axes are parallel to the rotation axis A-A of the block. Each cylinder 17 includes a cylinder port 18 opening into the surface 16, the ports 18 being arranged to cooperate with the main pressure port 5 during rotation of the cylinder block 15. At a position remote from the surface 16, the cylinder block includes an integrally formed skirt 1') around which is formed a cylindrical bearing surface 21 which effectively surrounds the cylinder block. Within the casing 2 adjacent to the cylindrical bearing surface 21 an internal cylindrical bearing surface 22 is formed which directly engages the cylindrical bearing surface 21 of the block to locate the block for rotation.

Five passages 24 are formed within the cylinder block one between each adjacent pair of cylinders. Each passage opens from the surface of the block remote from the valve surface 4 between the radially directed vanes 25 formed on the cylinder block 15 within the casing 2. A groove 26 is formed in the valve around the valve surface 4, one end of this groove connecting to the low pressure arcuate inlet port 30 formed in the valve surface 4.

The casing 2 remote from the valve includes a pair of integrally formed bosses 27 bored transversely to produce a pair of spaced apertures 28. Between the bosses 27 a swash plate 29 is mounted on a shaft 31 by means of a cylindrical bore 32 extending through the swash plate. The swash plate includes a flat swash surface 33 facing the cylinder block 15. Within each cylinder 17 a piston 34 and a compression spring 35 are located, the spring acting to urge its piston outwardly from the cylinder.

At its outer end each piston 34 is formed with a spherical socket 36 into which a ball 37 is secured. The ball 37 is integrally connected to a slipper 38 engaging the swash surface 33. A hydraulic passage 39 within each piston 34 gives access to the socket 36 for lubrication and also connects to passage 41 in the ball which feeds at pressure through a restrictor 42 to a recess 43 in the slipper surface in contact with the swash surface 33. The recess is conventionally arranged so that hydraulic pressure acting in the recess will almost completely balance the hydraulic load acting on the piston.

A retaining plate 44 includes five apertures 45 engaged one on each slipper 38. Centrally the retaining plate 44 reacts against a ball 46 carried by a pad 47 slidably mounted in a central bore in the cylinder block, a compression spring 49 reacting between the block and the pad 47 and serving simultaneously to urge the block against the valve surface 4 and to urge the retaining plate 44 to maintain the slippers in contact with the swash surface.

A splined aperture 51 is provided centrally within the cylinder block to open into a comparatively large aperture 52 extending through the valve 1. A drive shaft (not shown) may be inserted through the aperture 52 to engage the splined aperture to drive the cylinder block. A seal 53 may engage between the valve and the cylinder block in the manner disclosed in our co-pending application No.: 32,109/68, US. Ser. No.: 838,607. To prevent hydraulic leakage between the bore 48 and the aperture 52 the bore 48 is sealingly closed by means of a plug 54.

The servo cylinder 3 has a servo piston 55 slidably mounted therein one end being connected by means of a pivot pin 56 to a link 57 which in turn is connected by a pivot pin 58 to a lever 59 extending from the swash plate 29. In FIG. 1 the swash plate is shown at a position of maximum inclination and the servo piston 55 is in a corresponding position.

The small diameter bore 61 within the piston 55 receives one end of a rod 62 which extends from the end of the servo cylinder 3 adjacent to the valve 1. The end of the cylinder 3 adjacent to the valve 1 has a plug 63 inserted therein being retained in position by a cap 64 and circlip 65. A central bore 66 through the plug 63 locates the rod 62 for sliding movement, a suitable seal on the rod 62 preventing leakage of liquid. The end of the cylinder 3 adjacent to the valve 1 is formed in an extension 67 from the valve 1 but integral therewith. A rotary controlled spindle 68 is suitably mounted in bearings in the extension 67, the spindle 68 carrying a lever 69 which extends into a chamber 71 within the plug 63 to engage in a recess 72 in the end of the rod 62 such that rotation of the spindle 68 will cause endwise movement of the rod 62. A passage 73 extends in the valve 1 from the delivery passage 6 to intersect the cylinder bore 3. At the position of intersection the plug 63 includes a peripheral groove 74 from which a small hole is bored to form the restrictor 75 which connects through passage 76 in plug 63 to the working space 77 between the plug 63 and the piston 55.

The end of the rod 62 includes a counter bore 78 from which a pair of radially directed control ports 79 open into the working space 77. The rod 62 is located for limited motion within the piston bore 61 by means of a transverse pin 81 loosely engaging a transverse hole in the rod 62. The movement permitted for the rod 62 relative to the piston will vary the opening of the port 79 over the edge of the bore 61 into the working space 77. The ports 79 and the co-operating edge of the bore 61 form a variable restrictor adjustable by movement of rod 62.

The end of the servo bore 3 opposite to the valve 1 is formed as a screw-threaded inlet connection 82 and liquid entering connection 82 may pass into the casing through a cut-away portion 83 through which the lever 59 extends to the link 57. The liquid entering the pump thereby flows firstly over the swash plate 29 before entering the passages 24.

FIG. 3 of the accompanying drawings shows the flat end surface 16 of the cylinder block in elevation. The splined central hole 51 is surrounded by the fiat block surface 16 which contains the cylinder ports 18, the fiat surface 16 being interrupted by a co-axial circular groove 88 radially located in between the aperture 51 and the cylinder ports 18. The surface 16 is surrounded by an annular fiat surface 89 parallel to but slightly lower than the fiat surface 16. The annular surface 89 includes a plurality of shallow recesses 91 which define between them the axially extending vanes 92 for propelling liquid.

The annular surface 89 fits over the groove 26 (FIG. 4) formed around the flat valve surface 4. The groove 26 is closed by a wall 93 which extends from the valve surface 4 across the groove 26 and connects to a land 94 to reduce the width of the groove 26 at the end portion thereof adjacent the wall. The groove 26 at its narrowed portion connects to one end of the low pressure inlet port 30. As seen in FIG. 5 the groove 26 starts at a shallow depth at the wall 93 and gradually increases in depth around the valve surface 4, maximum depth of the groove being obtained at the position of entry to the inlet port 30. The narrowed part of groove 26 adjacent to the land 94 increases more greatly in depth than the remainder of the groove 26.

The seal 53 is seated in an annular recess 95 formed in the centre of the valve 1 so that the seal 53 can engage the flat portion of the block surface 16 between the central aperture 51 and groove 88. The outer edge of the recess 95 is chamfered at 96 so that a portion of the recess 95 radially outwards of the seal 53 makes connection with the annular groove 88 in the cylinder block surface 16. A shallow channel 97 in the valve surface 4 connects from the recess 95 into the inlet port 30 whereby liquid at low pressure built up in the inlet port 30 may enter the recess 95 around the seal 53 to retain a low backing pressure at the seal 53 to help to prevent induction of air from the aperture 52 across the seal and into the pump.

In operation the cylinder block is rotatably driven by a drive shaft inserted through the aperture 52 into the cylinder block and rotation of the cylinder block causes reciprocation of the pistons in the cylinders by virtue of the fact that the slippers are held by springs 35 and 49 against the swash plate surface. During rotation liquid fed from the inlet connection 82 flows around the swash plate and into the passages 24 there being induced by centrifugal pumping action to flow to the groove 26. The rotation of the cylinder block surface 89 over the groove 26 will by virtue of the vanes 92 induce flow of liquid around the groove 26 and into the inlet port 30. The vanes 92 acting on the liquid in the groove 26 will do so by virtue of the viscosity of liquid and it will be appreciated that the actual velocity of liquid flowing around the groove 26 will be considerably lower than the velocity of the cylinder block over the groove even when the pistons have their maximum stroke.

The total pressure build up at the inlet port 30 therefore results from the centrifuging action of the passages 24 and vanes 25 of the cylinder block and further from the impelling action of the vanes 92 on liquid in groove 26 by virtue of the viscosity of the liquid. The pressure of liquid in the inlet port 30 whilst still comparatively low will nevertheless provide an adequate boost pressure to assist the entry of liquid into the cylinders 17 during outward movement of the pistons 34. It will be understood that for the direction of rotation of the cylinder block, pistons in cylinders connected to the inlet port 30 will be moving outwardly from their cylinders whilst pistons in cylinders connected to the delivery port 5 will be moving into their cylinders to compress the liquid and deliver it to the port 5.

During rotation of the cylinder block there is a tendency for a reduced pressure to be developed in the recess 95 around the seal 53 due to centrifuging action of the cylinder block on the liquid. The channel 97 which connects the inlet port 30 to the recess 95 supplies liquid at the pressure in the inlet port 30 to the recess 95 and will increase the pressure in the recess to a small extent and prevent the tendency for air to be induced to enter into the pump between the seal 53 and the cylinder block surface 16.

The fact that the swash plate is inclined causes considerable side thrust to be exerted on the cylinder block through the pistons and the axial extent of the bearing surfaces 21 and 22 is such that the line of action of side force exerted on the pistons by the swash plate will pass directly through the bearing surfaces without creating tilting movement of the cylinder block. The flow of liquid through the passages 24 will assist in cooling the bearing surfaces 21 and 22.

The offset relation of the shaft 31 having regard to the rotation axis A-A of the cylinder block results in a torque being generated on the swash plate 29 about the axis of shaft 31 which will tend to reduce the inclination of the swash plate to zero, the limit of such movement being the engagement of head 84 of rod 62 against the cap 64. Maximum inclination of the swash plate is limited by the engagement of the head 84 against the end of chamber 71 opposite to the cap 64. The required angular setting for the swash plate is selected by the spindle 68 which adjusts the axial position of the rod 62. Movement of the rod 62 will adjust the variable restrictor formed by port 79 to control the pressure developed within the working space 77 by virtue of the series connection of the fixed restrictor 75 with the variable restrictor between the high pressure connection 76 and the low pressure interiorly of the casing 2. The pressure within the working space 77 urges the swash plate towards its maximum inclination whilst the torque developed on the swash plate itself urges it to the minimum inclination. Simple adjustment of the spindle 68 will therefore control pressure in the working space 77 to cause the swash plate to take up an angular position which is in proportion to the angular setting of the spindle 68.

During manufacture the passage 73 is formed by drilling from the exterior of the casing and in use the plug 85 closes the outer end of the passage 73. The passage 73 connects high pressure only to the groove 74 of plug 63.

The grade of aluminium alloy selected for the structural member forming the casing, the valve, the bosses and the servo cylinder is chosen to have the necessary strength to cater for the intended operating pressures of the pump. The design of the ports and in the valve in combination with the cross-sectional areas of the pistons is such that the cylinder block in operation presses only very lightly against the valve surface 4, the principal force holding the block on this surface being that provided by the springs and 49. During rotation of the cylinder block the centrifugal pressure of liquid developed around the cylinder block and the further pressure of liquid built up in the groove 26 particularly in the narrow part thereof adjacent to land 94 produce a force on the cylinder block dependent on speed which operates against the loading applied by the springs and 39 and when the pump is driven in excess of a predetermined speed causes the cylinder block to lift away from the valve surface 4 to reduce the pumping effect and also to increase flow of liquid over the valve surface 4 to provide better lubrication. A protection is thus offered against damage to the valve surfaces due to pick-up" when the pump is driven at high speeds.

1 claim:

1. A pump comprising a rotary cylinder block having cylinders disposed either parallel to or slightly inclined to the rotation axis, a cam device, pistons in the cylinders cooperating with the cam device whereby the pistons will reciprocate during cylinder block rotation, valve means cooperating with the block to connect the cylinders during cylinder block rotation alternately to a fixed high pressure port and to a fixed low pressure port in the valve means, said low pressure port subtending a substantial angle about said axis, a casing at least partially enclosing the valve means and cylinder block, a substantially arcuate groove in said casing adjacent the valve means facing towards a surface of the cylinder block, a connection directly between the said low pressure port and the said groove and means adapted to feed liquid into the casing whereby liquid may enter the said groove, liquid between the said surface of the block and the groove moving through the said groove by rotation of the cylinder block to increase liquid pressure within the groove thereby to pump liquid into said low pressure port, the flow of said liquid from said low pressure port to said groove being continuous during pump operation thereby continuously to supercharge the liquid in said low pressure port.

2. A pump as claimed in claim 1 wherein the groove substantially surrounds the valve means and includes a terminal wall adapted to direct liquid from said groove radially into the low pressure port.

3. A pump as claimed in claim 2 wherein the said groove increases in depth in the direction of cylinder hlock rotation and reaches its greatest depth adjacent to the end wall.

4. A pump as claimed in claim I wherein the valve means has a flat surface co-opcraling with a flat surface of the block adjacent to the said surface.

5. A pump as claimed in claim 4 wherein the said groove surrounds the flat valve surface and includes a terminal wall adapted to direct liquid from the said groove radially into the low pressure port.

6. A pump as claimed in claim 5 wherein the said groove increases in depth in the direction of block rotation and reaches its greatest depth adjacent the said wall.

7. A pump as claimed in claim 6 wherein a part of the groove adjacent to the said wall is of reduced width compared with the remainder of the groove.

References Cited UNITED STATES PATENTS 3,170,297 2/1965 Larson 91-485 3,036,434 5/1962 Mank 60-53 A 2,543,624 2/1951 Gabriel 91485 2,284,111 5/1942 Vickers 91-485 1,427,740 8/1922 Johnson 9l5(]7 WILLIAM L. FREEH, Primary Examiner US. Cl. X.R. 9l--487 

